My kind of thinking there. I've had similar sinister thoughts for a long time now, using lower jaw section from cattle or a shoulder blade for a buttstock, hip bone or humerus for the tiller, some other bits fitted to make the pistol grip...haaa! That's some fun stuff!

Spine alone though might be a bit of a challenge. Perhaps you can do a skeletized frame from some maple ply to pin the bones to (it will be easier to mount the trigger/prod onto a frame) and then smooth the frame to bone connection with some putty?

Another fun thought would be to sculpt some floral/scroll appliques onto the bare sections of the frame and then paint them int some accenting color (off white stock, red scrolls / off white stock, black scrolls...I mean it's a thing of taste...in fact I think apoxie sculpt already comes in different shades, so you have some options ).

All in all, I love it! It's a real cool idea and will take or make an artist to execute. Definitely wishing you luck on this one.

Lets see some pictures of the spine you got and maybe we can draw up and explore some sketches for more ideas.

With a little bit of fiddling, you can probably fit the spine over the back of the *staff? * and carve the tip into a claw shape. A little skull (coyote maybe) fitted over the nut would look sweet too.

...perhaps you can even do the trigger lever encased in bone...just thoughts.

Da Vinci ~ Desert experience.

Who seen my snake skin turban?

Ivo

PS: Now that I think about it...the *CLAW* might be a bit too much. ...and will make spanning the bow a *little* uncomfortable. ....I get carried away, please procede.

So I played a bit with FAD (Foamcore Aided Design) and made a mockup of the mechanics of the crossbow I like. Hopefully test a few geometry things out before getting to the real build material (and saves countless hours when I add the decoration).

What do you all think so far?

I think I am going to adjust the air piston to some heavy gate springs I have (x4) and make the tension based on extension instead of compression. Now just have to figure out how.

A bit of reference wont hurt and will help everybody:This very interesting crossbow was design and patented by a master crossboyer Robert Van House in 1977. Richard Middleton mention him in his reference book "Man Powered-bullet"Quote:"At the American Crossbow Association's speed contest in 1978 Van House recorded a velocity of 370fps with a spring-powered version, and later shooting the same crossbow he achieved 427fps" "Again,it is worth noting that hight velocities result from a long draw"In the brevet he also draw a gaz powered version planned to produce lot more speed.

Can't upload them to the tube for some reason, so here's my photobucket deal.

This is with the *push* rods.(like on the original)

This is with the *pull* rods.(I just flipped the levers there)

And this is side by side.

I didn't really go into the deal with which is more efficient, just set everything up to run the same speed (one video just lagged, but side by side worked ok)

All in all, the whole deal with converting from compression spring to extension is throwing the spring over to the other side of the rods. Like so...

A similar setup can be seen on this little flipper bow where the rubber bands are up front and pulling on the cables.

But, I'm not too fond of "push rods", the deal is that a structure that supports weight has to be strong enough to withstand the load in compression...while to suspend the same weight teh structure can be substituted by a cable or a rod only strong enough to withstand the load in tension. Basically we're comparing here a chair leg and a piece of rope...which one is heavier?

Same here, the weight of this transitional piece has to be accounted for when designing a bow....so to cut it short - I really like the system with a "pull rod" or "cable" (like in the second video and on the flipper.) because it's lighter and that will already boost the bows performance....not to mention the power storage for it...if rubber is used (though not as consistent as a metal or gas spring) even more weight will be cut down resulting in further improvement.

I've thought about the construction of this bow too, personally I'd make it all out of metal ( ), but considering it's going to be a rather light bow I think some thin plywood will suffice (maybe some dense 1/4" or 3/8") with some holes drilled in the levers to lighten them. I actually started drawing up a set of plans and making a 3d model for it, alas I'm out of time for the day...maybe I'll put some more work in tonight.

"Again,it is worth noting that hight velocities result from a long draw"

Yeh, this bow has some seriously draw length. Even if made light, it will put out some nice numbers.

Now that I think about it...Tallisman's Mantis comes to mind too.(whiteraven, that little bow in your facebook album is mantis's baby brother, "Devil Claw" I thin is his name )

That's it for now, I've depleted my forum time, will be back later to check on the situation.

I'm just biased...no matter how hard I try to just flow with the variety of tastes, I keep coming back to my cursed way of thinking >>> gotta make it compact, gotta make it compact and powerful...and so on and so forth till I need a reset.

Did you have any trouble understanding the bit about switching the system to extension spring? I kinda feel like I might have went a bit overboard with the explanation...not all are born poets so to speak.

Ivo

PS: Personally, I'm looking forward to see how this project turns out, no matter what systems you choose or how long the draw will be. It's all about having fun building a shooter and busting some holes in things, right?

This is what I was thinking as far as the tension on the bow. The red is the main drive tension, including the gates springs and I think I'll use the surgical rubber tubing?The blue is the propulsion drive, that transfers the kinetic power to the bolt upon firing.

After doing the staff version...I just couldn't leave it at that and made a bull-pup version as well (the regular version is in the patent).

Didn't add the strings and the spring dimensions/position is not important ,as everyone will be using whatever they can get their hands on...same with the axels/fasteners/connections. (also the draw length I just guessed...what would be the fun in making an accurate blueprint, right? )

As you can see, the 3d view shows a pretty bulky front end that will make this thing look like gravity hammer (from halo ) if made like a staff...also, at teh moment Ican't imagine how one would span a staff based crossbow, but I might just be lacking imagination.

Program needed to view the model is Sketchup.

http://sketchup.google.com/download/

Enjoy.

PS: I'm no perfection, everyone welcome to chip in on the model if I missed something or made a mistake...I plan to edit/improve it in time.

Last edited by Ivo on Tue May 29, 2012 4:31 pm; edited 1 time in total